A multilayer color photographic light-sensitive material must have each coupler fixed in a separate layer in order to reduce color mixing and improve color reproduction. Many methods for rendering a coupler diffusion-resistant are known. One method involves introducing a long chain aliphatic group into a coupler molecule in order to prevent diffusion. Couplers produced by this method must be added to an aqueous gelatin solution by solubilizing in alkali, or by dispersing in an aqueous gelatin solution by dissolving in a high boiling organic solvent, since the couplers are immiscible with an aqueous gelatin solution.
Such color couplers may cause crystal formation in a photographic emulsion. When using a high boiling organic solvent, a large amount of gelatin must be employed since the high boiling organic solvent makes the emulsion layer soft. This is counter productive to the requirement that the thickness of the emulsion layer be reduced.
Another method for rendering a coupler diffusion-resistant is to utilize a polymer coupler latex obtained by polymerization of a monomeric coupler. An example of a method of adding a polymer coupler in a latex form to a hydrophilic colloid composition is a method in which a latex prepared by an emulsion polymerization method is directly added to a gelatino silver halide emulsion. In another method a lipophilic polymer coupler obtained by polymerization of a monomeric coupler is dispersed in a latex form in an aqueous gelatin solution. Examples of the former emulsion polymerization method are described in U.S. Pat. No. 3,370,952 4,080,211 which respectively describe disbursements in an aqueous gelatin phase and water. An example of the latter method in which a lipophilic polymer coupler is dispersed in a latex form in gelatin is described in U.S. Pat. No. 3,451,820. The method of adding a polymer coupler in a latex form to a hydrophilic colloid composition has many advantages in comparison with other methods. For example, the deterioration of strength of the film formed is small, because the hydrophobic substance is in a latex form. Also, since the latex can contain coupler monomers in a high concentration, it is easy to incorporate couplers in a high concentration into a photographic emulsion, and the increase of viscosity is small. Furthermore, color mixing is completely prevented, since a polymer coupler is immobilized and the crystallization of couplers in the emulsion layer is small. In particular, when the polymer coupler latex prepared by an emulsion polymerization method is used, the step of adding the coupler to a coating solution can be simplified, since the use of a high boiling organic solvent or an alkali is not necessary and a special dispersing method is not required. Moreover, the thickness of the layer can be reduced, since an organic solvent is not contained therein.
The addition of these polymer couplers in a latex form to a gelatino silver halide emulsion are described, for example in U.S. Pat. Nos. 4,080,211, 3,370,952 and 3,451,820, a copolymer latex with a competitive coupler in West German Pat. No. 2,725,591, and a cyan polymer coupler latex in U.S. Pat. No. 3,767,412.
However, these polymer coupler latexes have a number of problems in addition to the many advantages described above. It would of course be desirable to overcome these problems. The problems include the following:
1. The light fastness of the magenta color image is very poor.
2. Undesirable fog is readily formed upon color development.
3. The fastness to humidity and heat of the color image is poor.
4. The aggregation of latex occurs in a solution.
Various methods for the prevention of fading of a magenta color image caused by light have been provided. Of these methods, the method in which a phenolic compound provided for an oil-soluble magenta coupler is used together with a coupler is extremely effective. Useful phenolic compounds include alkoxy or aryloxy phenols, hydroxycumaranes, hydroxychromans and dihydroxyspirochromans as described in U.S. Pat. No. 3,432,300, 3,573,050, 3,574,627 and 3,764,337, West German Patent Application (OLS) No. 2,146,668, etc. Furthermore, in order to prevent the reduction of color density obtained due to these phenolic compounds, the use of a hydroquinone together with the phenolic compound is described in Japanese Patent Application (OPI) No. 14023/76 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
However, when the above described compounds are dissolved in water or an organic solvent such as a lower alcohol and then added to a polymer coupler latex, or the compounds are added thereto as a dispersion, the compounds do not improve fastness to light to the same extent that they provide the effect to the oil-soluble magenta couplers. Further, other disadvantages are encountered. For example, a yellow stain may be formed in the areas of no or low optical density, the color hue may be adversely affected, fog may be formed, inferior dispersion may be obtained, or crystals may be formed. Therefore, a stabilizer for a color image which exhibits collectively superior effects for photographic use has not yet been found.